A first known control device of this kind is described in US 2006/0254377. The stick is driven about two perpendicular pivot axes (A, B) by respective rotary actuators. A balance weight is provided on the A-axis in order to provide vertical mass balance about the B-axis. In other words, the balance weight ensures that there is no net induced moment about the B-axis when the device is subjected to a vertical acceleration perpendicular to the A and B axes.
A first problem with this arrangement is that the balance weight adds to the total weight of the device. A second problem is that the balance weight adds to the total volume of the device. A third problem is that the device is not horizontally mass balanced. Therefore, if the device is subjected to a horizontal acceleration, then there will be a net induced moment about the A or B axis. This mass imbalance must be compensated by one or both of the actuators, which adds complexity to the system.
A second known control device of this kind is described in U.S. Pat. No. 6,708,580. This device is also not horizontally mass balanced.